Monitoring per DHCP client network traffic

Hello,

I'd like to find a piece of SW that runs from my laptop that will monitor my wireless router and tell me how much data each DHCP client is consuming, preferably live and in the form of a graph. I have the following:

For now I'm looking at the Status/Bandwidth screen in DD-WRT and have QoS turned on and set for:
Wan Up 1750kbps
WAN Down 1750kbps
LAN 1000000kbps

Even with these settings I'm seeing 10Mbps data spikes at regular intervals and have tracked it down to the Roku my son is watching. How is this possible with the current QoS settings??? I shut down Roku and levels drop to the background at 25-150Kbps.

My concerns are that while Cox has not complained yet. This month we burned through the normal 250GB allowance in 19 days. Some of my equipment (Smart DVR) will play episode after episode of TV programs for hours on end if someone walks out of a room and forgets they're running. Roku is really good at this. I know some of the bandwidth went to multiple Ubuntu images I downloaded. I want to watch the network for, say a week, and see where most of the data is directed so I can address whether it's appropriate, or simply waste.

Regarding the 10Mbps spikes, if I tell the router to limit traffic to/from any DHCP client to 1.7 Mbps, I don't EVER expect to see it allow traffic faster than this. At 1.7 Mbps, we still get acceptable image quality even when 3 or 4 clients on the network are simultaneously downloading video content at their prescribed limit. One of the biggest reasons I set the limit was because I would see one client grab almost all the bandwidth, my Sony DVR in the living room is the worst culprit, and refuse to surrender any when other clients attempted to connect.

I am sorry to hear that there doesn't seem to be a SW way to accomplish this "per DHCP client" monitoring and wondered if I flashed a full version of DD-WRT to the Buffalo router, this might not be possible. I've seen software advertised online that does this, but I don't see it as a problem requiring an $1,800 answer. Is there a consumer level wireless router capable of this level of monitoring?

As you seem to have a separate router and modem you could put something like m0n0wall between the router and modem.
The Buffalo firmware has SNMP, so you may be able to use the free version of PRTG to monitor the unit.